This invention relates generally to centrifugal separators and, more particularly to improvements in flight design which extend the useful life of various components within the separator while decreeing its maintenance.
As is well known, centrifugal separators are widely used in a variety of processes in which material separation is required. Typically, material is fed into a top of the separator and is brought into contact with rotating elements within the separator. Solid material is retained near the center of the separator by perforate plate or profile bar screens while free liquids are slung through the screen by centrifugal force, to the outside of the separator. These liquids then are directed to a drain outlet and the solid material falls, by gravity, to the bottom of the separator where it is discharged for collection.
Because of the abrasive quality of the material fed into the separator, and the impact forces which are created as the material is moved through it, components within the separator are subject to rapid wear. Screens, rotors, flights, etc. all need to be replaced with such frequency that the separator has substantial down time while necessary maintenance is being performed.
The maintenance problem with centrifugal separators has long been recognized and different measures have been undertaken to address it. In U.S. Pat. No. 4,961,722, for example, a screen assembly is described having separate upper and lower portions. These portions are separate became in conventional centrifugal separators, the screen assembly projects as far upwardly within the separator housing as the flight assembly of the separator which is mounted in the screen. In use, material introduced into the separator is flung against the screen by the rotating flight assembly and then travels by gravity and centrifugal force down the flight assembly. Because of the impact forces of the material against the screen, the upper portion of the screen, which is in general horizontal alignment with the upper end of the flight assembly, rapidly becomes worn and needs frequent replacement. U.S. Pat. No. 4,961,722 discloses a separable upper and lower screen portion which facilitates replacement of the screen portion subjected to the greatest wear, thus reducing down time and maintenance costs since only part of the screen is replaced requiring limited tear down of the inner mechanism of the separator.
U.S. Pat. No. 5,256,289 discloses an improvement in a separator that includes a pocket assembly positioned between a discharge port of the material inlet assembly and the upper end of the flight assembly. The pocket extends radially outward beyond an upper end of the flight assembly. A lower end of the pocket assembly extends below the upper end of the flight assembly, and the upper end of the semen is integral with the lower end of the pocket assembly. The pocket creates a basket for catching material introduced into the separator through the inlet assembly. The pocket replaces the upper portion of the screen, which previously was used to catch this material. Since the material impacts against a sidewall of the pocket assembly rather than against the screen, the useful life of the screen is greatly extended.
Despite any improvements provided by the prior art, the screens within centrifugal separators take a tremendous beating by the solid materials flung against them during use. Attempts to improve screen life primarily have involved modifications or improvements in the screen itself. It would be useful, therefore, to take a different approach to the problem of premature or excessive screen wear by improving aspects of the flight assembly, which actually accelerates the incoming solid material to reduce impact forces and thus abrasion against the screen, in order to improve the useful life of the screen.